Abstract

Background

Secreted modular calcium binding protein-1 (Smoc-1) belongs to the BM-40 family which has been implicated with tissue remodeling,
angiogenesis and bone mineralization. Besides its anticipated role in embryogenesis,
Smoc-1 has been characterized only in a few mammalian species. We made use of the consensus
sequence (5' CACCTCTCCACCTGCC 3') of 33.15 repeat loci to explore the buffalo transcriptome
and uncovered the Smoc-1 transcript tagged with this repeat. The main objective of this study was to gain
an insight into its structural and functional organization, and expressional status
of Smoc-1 in water buffalo, Bubalus bubalis.

Results

We cloned and characterized the buffalo Smoc-1, including its copy number status, in-vitro protein expression, tissue & age specific transcription/translation, chromosomal mapping
and localization to the basement membrane zone. Buffalo Smoc-1 was found to encode a secreted matricellular glycoprotein containing two EF-hand
calcium binding motifs homologous to that of BM-40/SPARC family. In buffalo, this
single copy gene consisted of 12 exons and was mapped onto the acrocentric chromosome
11. Though this gene was found to be evolutionarily conserved, the buffalo Smoc-1 showed conspicuous nucleotide/amino acid changes altering its secondary structure
compared to that in other mammals. In silico analysis of the Smoc-1 proposed its glycoprotein nature with a calcium dependent conformation. Further,
we unveiled two transcript variants of this gene, varying in their 3'UTR lengths but
both coding for identical protein(s). Smoc-1 evinced highest expression of both the variants in liver and modest to negligible
in other tissues. The relative expression of variant-02 was markedly higher compared
to that of variant-01 in all the tissues examined. Moreover, expression of Smoc-1, though modest during the early ages, was conspicuously enhanced after 1 year and
remained consistently higher during the entire life span of buffalo with gradual increment
in expression of variant-02. Immunohistochemically, Smoc-1 was localized in the basement membrane zones and extracellular matrices of various
tissues.

Conclusion

These data added to our understandings about the tissue, age and species specific
functions of the Smoc-1. It also enabled us to demonstrate varying expression of the two transcript variants
of Smoc-1 amongst different somatic tissues/gonads and ages, in spite of their identical
coding frames. Pursuance of these variants for their roles in various disease phenotypes
such as hepatocellular carcinoma and angiogenesis is envisaged to establish broader
biological significance of this gene.